How to Configure eBGP and iBGP with Peer-Groups
BGP (Border Gateway Protocol) with peer-group configurations
Objective
This document explains how to configure eBGP (External BGP) and iBGP (Internal BGP) using peer-groups on routers. Peer-groups help simplify BGP configuration by grouping neighbors with common policies, reducing repetitive commands and improving scalability.
Prerequisites
Hardware:
Switches or routers that support VLANs
(e.g., edgecore, ufispace)
Software:
Network operating systems that support VLAN configuration
(e.g., SONiC-OS-4.4.0-Enterprise_Base, SONiC-OS-4.4.2-Enterprise_Base)
Access:
Administrative or privileged CLI access
Network:
Established IP connectivity between BGP neighbors.
Public or private AS numbers, IP addresses for peerings, and agreed routing policies.
Topology Diagram
Example:
Two routers configured as BGP neighbors exchanging route information.
Basic Configuration Steps
1. Define Local and Remote AS
For eBGP, set the local AS and the neighbor’s external AS.
For iBGP, set both neighbors with the same AS number.
2. Configure Peer-Group
Create a peer-group to group neighbors sharing the same configuration (timers, route policies, etc.)
3. Assign Neighbors to Peer-Group
Add neighbor IP addresses under the peer-group to inherit common settings.
4. Advertise Networks
Specify local networks to announce into BGP.
5. Apply BGP Policies (Optional)
Configure route-maps, prefix-lists, or filters to control route advertisement and acceptance.
Example Configuration (DUT_1 and DUT_2)
DUT_1
configure terminal
ip prefix-list ALLOW seq 10 permit 192.168.1.1/24
route-map ALLOW_LOCAL_NET permit 10
match ip address prefix-list ALLOW
router bgp 65100
router-id 11.11.11.11
log-neighbor-changes
timers 60 180
!
peer-group INTERNAL
remote-as internal
timers connect 30
advertisement-interval 0
!
address-family ipv4 unicast
activate
route-map ALLOW_LOCAL_NET in
send-community both
!
neighbor 10.0.0.2
peer-group INTERNAL
DUT_2
router bgp 65100
router-id 22.22.22.22
log-neighbor-changes
timers 60 180
!
peer-group INTERNAL
remote-as internal
timers connect 30
advertisement-interval 0
!
address-family ipv4 unicast
activate
route-map ALLOW_LOCAL_NET in
send-community both
!
neighbor 10.0.0.1
peer-group INTERNAL
Verification
show ip bgp summary #shows bgp neighbors
show bgp ipv4 unicast summary #show bgp neighbor status
show bgp ipv4 unicast neighbor <neighbor_ip> advertised-routes
#check the advertise routes are correct
Troubleshooting Tips
Ensure both sides have matching AS numbers (iBGP: same, eBGP: different).
Verify IP connectivity between BGP peers.
Confirm peer-group settings are properly applied.
Check for BGP session establishment issues using show ip bgp neighbors.
Review route policies or filters if routes are missing.
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